Edinson Volquez believes a tiny blister on the inside of the thumb of his throwing hand led to his worst outing of the season Saturday night.

The blister caused him discomfort. That led to an adjustment to work around the discomfort. Which led to his mechanics going haywire. Which resulted in defeat.

“It was a tough day,” Volquez said after the New York Mets took advantage his control problems to score four runs in the second inning en route to a 6-2 victory over the Padres before 36,826 at Petco Park.

“I felt different tonight.”

He looked different – and nothing like the pitcher who was 4-0 with a 2.36 earned run average over his previous seven starts.

Volquez’s 23rd start of the season was his shortest.

He lasted only 1 2/3 innings, giving up four runs on two hits and four walks. Only 25 of the 54 pitches thrown by Volquez were strikes. Previous to Saturday night, Volquez hadn’t pitched fewer than five innings in any of his starts.

Volquez retired the Mets in order in the first. But he said he first felt the blister while striking out Jordany Valdespin.

Volquez then came apart in the 43-pitch second, walking four of the eight batters he faced, including two with the bases loaded.

Walks and mechanical issues are nothing new to Volquez. He has blown hot-and-cold throughout his career and walks have always been a problem. He’s actually been smoother this season.

He leads the National League with 80 walks this season – at a rate of 5.3 walks per nine innings – and has an outside shot of topping the club record of 125 set by Matt Clement in 2000.

But he hadn’t before missed like he was missing Saturday night.

“His mechanics were out of whack by as much as anything I’ve seen this season,” said Padres manager and former pitching coach Bud Black. “In spurts, we’ve seen his mechanics betray him a bit.

“I felt a little more uncomfortable there than I have in the past. I felt it might not get better.”

Which is why Black pulled Volquez after only 54 pitches. There were no signs that things might get better. And it looked like it could get worse.

“The inning was still going on,” said Black of the Mets decisive second.

After Andres Torres struck out, Volquez walked catcher Josh Thole to force home the game’s first run. Then, after striking out Hefner for the inning’s second out, Volquez issued a second bases-loaded walk to Ruben Tejada in front of a two-run double by Valdespin.

The two bases-loaded walks were the fourth and fifth issued by Volquez this season and brought the Padres total of bases-loaded walks issued to 15.

“This is nothing that can’t be easily fixed,” said Volquez, who has spent considerable time with Padres pitching coach Darren Balsley this season refining his mechanics. “It’s nothing big. Every pitcher has one of these sometimes. The blister got in my mind.”

Due to Volquez, Black had to use five relievers, with Cory Burns, 24, pitching 1 2/3 innings in his major league debut.

It was a big night for two former Padres prospects.

Right-handed starter Jeremy Hefner, who was waived off the 40-man roster last November, held the Padres to one run on five hits over six innings to pick up his second major league win. And outfielder Baxter, who played briefly with the Padres in 2010, tied a Mets single-game record by drawing five of the season-high 10 walks issued by Padres pitchers.

Alexi Amarista had three of the Padres six hits and drove in the Padres first run. Everth Cabrera had two hits and scored a run. Third baseman Chase Headley hit his 14th homer of the season leading off the ninth for the Padres second run.